Against the backdrop of climate change, the reduction of harmful substances in the atmosphere is a worldwide goal. This applies in particular to the emission of carbon dioxide (CO2), which accumulates in the atmosphere, preventing the excess heat from escaping into space, and thus leads to an increase in the surface temperature of the Earth due to the so-called greenhouse effect.
In the case of fossil-fired power plants for the production of electrical energy in particular, the burning of fossil fuel results in the production of carbon dioxide-containing flue gas. In order to prevent or reduce the release of carbon dioxide emissions into the atmosphere, the carbon dioxide must be separated from the flue gas. In existing fossil-fired power plants in particular, suitable measures are therefore being considered in order to separate the carbon dioxide generated during combustion from the exhaust gas (post-combustion capture).
As a technical implementation to achieve this, carbon dioxide contained in the flue gas after combustion is washed out of the respective gas stream using a washing medium or an absorption medium in an absorption-desorption process. For this purpose, amine-containing washing media showing good selectivity and a high capacity for carbon dioxide are frequently used.
However, these amine-based washing media tend toward the buildup of nitrosamines. Small amounts of volatile toxic nitrosamines result from secondary flue gas components such as nitrogen oxides (NOx), and small amounts of volatile toxic nitrosamines can be formed because of the generation of small amounts of volatile amines formed by thermal decomposition or oxidative or catalytic breakdown of the washing medium.
The nitrosamines or amines accumulate in the washing medium until a stable equilibrium is reached between the rate of formation of decomposition products or secondary decomposition products (degradation products as a whole) and the rate of their removal from the process. The concentration of degradation products therefore increases over time as the separation process proceeds. Because of the large amounts of flue gas brought into the separation process and the accompanying accumulation of degradation products, these components may be released into the atmosphere via the absorber or contaminate the separated carbon dioxide.
In order to prevent these undesirable emissions, for example, a purification device may be used for the flue gas discharged from the absorber. For this purpose, single or multiple-stage aqueous scrubbers may be configured on the absorber which remove both volatile amines and produced nitrosamines from the carbon-dioxide-purified flue gas stream. However, for the large amounts of flue gases to be cleaned, which can amount to several million cubic meters of flue gas per operating hour, this method is time-consuming and expensive with respect to both investment and operating costs and structural expenditure.
Alternatively, it is possible to configure a purification device downstream from the desorber. A method of this type is known from WO 2013/023918 A1 in which highly volatile degradation products are removed from the absorbent circuit of a CO2 removal process. In this case, the CO2 removal process comprises the absorbent circuit with an absorber and a desorber, wherein condensate is removed from condenser downstream from the desorber and largely purified of degradation products. For this purpose, the condensate is supplied to a purification device in which the condensate is purified of the degradation products contained therein by means of distillation or using an activated carbon scrubber. The purified condensate formed in this manner is again returned to the absorbent circuit. However, the above-described method cannot be economically implemented under certain boundary conditions.
Furthermore, a method is known from EP 2559473 A1 for purifying a product of a process plant which is contaminated with nitrosamines. The contaminated product is treated with UV radiation, thus destroying the nitrosamines. In this case, the product to be purified is the CO2-containing solvent or washing medium contaminated with nitrosamines. According to EP 2559473 A1, one or a plurality of UV radiation sources may be used for irradiation, each of which is connected in a washing medium circuit to a line for a washing medium charged with carbon dioxide, so that the nitrosamines contained in the washing medium are destroyed by UV radiation. The resulting decomposition products can be removed, for example, using an adsorption device.